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S3 switches - what do they do


Ian Barrett

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Guys,

Can someone tell us what these switches are supposed to do.

You're probably aware my mate has just bought a S3 and in the short time we had to play with it we could only find out the bottom right is the fog light switch.

Reading on here about the BRAKE function has been interesting. Especially as it does nothing but I'm expecting to find his brakes are completely shot with the way it locks up the rears.

Thanks

IanB

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Hello matey,

The "Brake" light should be to indicate a pressure failure in the brake line. Being a LWB it should have dual circuit servo assisted brakes. When the pressure in one of the circuits drops (indicating a failure or fluid leak) the light should come on to warn you.

As for the locking up of rear brakes...well with nothing in the back, it's got no ballast and very little grip over the rear wheels so I'm not massively surprised!!

Tom

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Hello matey,

The "Brake" light should be to indicate a pressure failure in the brake line. Being a LWB it should have dual circuit servo assisted brakes. When the pressure in one of the circuits drops (indicating a failure or fluid leak) the light should come on to warn you.

As for the locking up of rear brakes...well with nothing in the back, it's got no ballast and very little grip over the rear wheels so I'm not massively surprised!!

Tom

The 109's brake failure warning light normally has three triggers, though some models also had a couple of others. The standard triggers are:

i) differential pressure between front and rear circuits;

ii) insufficient vacuum in servo;

iii) bulb test, either a test switch near the light or an automatic trigger between the warning system's relay and the ignition switch to test the system on engine start.

The other optional (fitted to certain export markets like Switzerland) triggers are the hand brake and an excess pedal travel switch on the top of the pedal box (*the latter may be for single-line systems in lieu of the differential pressure valve on dual circuit vehicles).

With regard to the switches, my 1982 109 has the same panel and had the brake warning light, rear fog switch and hazard switch on that panel, with the hazard switch next to the fog switch. It looks like the hazard switch has been replaced with an aftermarket one - the original is like the fog switch but illuminates internally. It's bulb contacts are very prone to bending and repairs are generally short lasting, but the switches are horrifically expensive. If the vehicle has any extra lights, they would likely be controlled by the upper right switch on that panel. An electric engine cooling fan seems a plausible explanation too.

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